Modelling THz TDS Spectra of Powder Compacts for Analysis of Pharmaceutical Oral Solid Dosages

THz TDS is a vital tool in many industrial sectors, however commonly analyzed samples are often produced as powders or granular materials; these morphologies have been demonstrated to produce anomalous spectral features which appear at unpredictable locations and can hamper spectral analysis. Here we systematically study the effects of sample morphology on the appearance of anomalous spectral features and present a physical mechanism to describe their behavior. Two-part powder compacts of PTFE and Borofloat glass are prepared at a range of microsphere sizes and concentrations for TDS measurement. Further, a computational model utilizing raytracing through heterogeneous material is developed, which is able to accurately predict the anomalous spectral features. By attributing a physical mechanism to this phenomenon, we are able to predict their occurrence, and utilize their presence to deduce sample morphology.